This invention relates in general to a method and apparatus for injecting additive into fuel products and, more particularly, to a system and method for controlling the flow of additive through an interchangeable additive injection apparatus providing a plurality of flow paths from one or more upstream additive tanks to one or more downstream fuel containers.
A well-known application for additive injection systems is a truck loading terminal wherein tanker trucks are filled with fuel for transporting the fuel to a further distribution site. A tank on the truck is filled primarily with a generic fuel product from a fuel supply pipe. As the fuel is loaded into the tank, one or more fluid additives may be injected into the fuel stream to form a blended mixture of additive and the generic fuel product. The additive is typically injected into a fuel load arm connecting the fuel supply pipe to the fuel tank. The recipient of the shipment of fuel loaded into the tanker truck will often preselect the particular additive and specify the quantity (or ratio) of additive desired for the blended fuel. Consequently, the generic fuel may become the proprietary product of a fuel marketing company by blending a particular additive with the generic fuel in a specified ratio.
Additive injection equipment is used to blend the additive with the generic fuel. It is important to provide an accurate dosage of additive for each individual batch. This requires careful measurement of the additive as well as timely control of additive flow. Otherwise, the equipment may continue to inject additive into the load arm after the fuel stream has terminated. If so, not only will the most recent batch of fuel have a lower ratio of additive to fuel, but a subsequent batch of fuel may unintentionally flush the additive remaining in the load arm into the fuel tank on the truck. The presence of this extra additive in the subsequent batch of fuel will adversely affect the desired additive to fuel ratio for that batch, which may call for a different additive altogether.
Typically, the prescribed additive is incrementally blended into the fuel stream at discrete intervals defined by a preselected ratio of fuel to additive. For example, a particular order may require the injection of one gallon of additive into the load arm after 40 gallons of fuel have been supplied to the load arm. A fuel meter on the fuel supply pipe measures the fuel supplied to the load arm and sends pulses representing the quantity of fuel supplied to the additive injection equipment. Upon receiving a predetermined number of such pulses, the additive injection equipment supplies one gallon of additive to the load arm. Thus, the prescribed dose of additive is cyclically injected into the fuel stream based on the preselected ratio.
In an existing additive injection system, each chemical additive tank includes a control panel having a microprocessor, a solenoid valve and a flow meter. One additional control panel is required for each additional fuel load arm to which the additive tank is coupled for injecting additive therein. These control panels control the flow of additive into the load arm in response to pulses received from the fuel flow meter, the pulses representing the quantity of fuel passing through the supply pipe as described above.
Alternatively, the additive may be continuously fed into the fuel stream in accordance with a predetermined additive to fuel ratio. For continuous injection, the injection of additive commences shortly after fuel begins to flow through the supply pipe into the load arm. Throughout most of the fuel loading process, the proportion of additive to fuel supplied to the fuel tank substantially adheres to the established ratio. However, the rate of additive injection should drop off sharply just prior to the termination of fuel flow through the fuel supply pipe. Otherwise, the previously addressed problem of additive remaining in the fuel load arm may occur.
Another problem associated with conventional additive injection systems is that the control panels, each with its own microprocessor, solenoid valve and flow meter, are an expensive investment. A relatively large number of these expensive control panels is required to enable the additive to flow from any one of a plurality of additive tanks to one or more fuel load arms. As an example, a fuel truck loading terminal with five additive tanks and two fuel load arms would require ten separate control panels, each additive tank requiring a separate control panel for each load arm serviced. Accordingly, the five additive tanks would require a total of ten microprocessors, ten solenoid valves and ten flow meters. Furthermore, when one of the valves or meters fails, the injection system must be shut down until the device can be repaired or replaced. Thus, in addition to the expense of replacement parts, a faulty control panel may cause significant downtime and require considerable operator time before the system can be repaired and is operating again.
Additive injection equipment may also be used to inject certain additives into fuel tanks in a retail setting, such as a service station. A service station may inject varying levels of additive from a single on site additive tank into several fuel tanks to create different grades of gasoline. Typically, each fuel tank at a service station will be associated with its own fuel supply pipe. The additive tank may be individually coupled with each of the fuel supply pipes so that a desired quantity of additive can be blended with the fuel supplied to any one of the fuel tanks. Each of the fuel tanks at the service station is also associated with a separate fuel pump accessible to consumers. Thus, a consumer may individually select a particular grade of gasoline based on the relative quantity of additive contained in the fuel.
By contrast to the wholesale systems employed at truck loading terminals, retail systems typically do not inject additive at intervals in response to the flow rate of fuel into the fuel tank because the flow rates are generally too high for the control panels to measure the pulses. Rather, most retail systems employ a batch process for injecting a preselected quantity of additive into the fuel supply pipe based on the quantity of fuel to be loaded into the fuel tank. For retail applications, fuel and additive are usually manually injected into the fuel tank, but it is not uncommon for an operator to use a computer or microprocessor to indicate the desired quantity of additive or fuel to be loaded just prior to manual injection. In any event, current retail injection systems are generally time and labor intensive and do not provide the accuracy and efficiency of automated injection systems.
An additional problem associated with the additive injection systems of the prior art arises when additive tanks or pipes are exposed to freezing temperatures. In this event, the additive contained therein may become stratified, undermining the injection process. One solution to this problem is to add diluents to the additive, which often increases the expense of the additive. However, it is preferable to avoid the use of diluents and blend concentrated additive with the fuel.